This invention relates to a device for preventing a belt from being pulled from a retractor, such as an inboard retractor at the center of a car in a passive vehicle occupant restraint system, after emergency locking of the belt at the time of collision of the car.
A conventional belt retractor commonly used in a vehicle occupant restraint system has an emergency locking machanism which prevents the belt from being pulled out upon the deceleration or acceleration of the car at the time of collision. This type of retractor, which is often called a lock retractor, usually operates by automatically preventing the belt reel of the retractor from rotating. However, when a strong pull-out force acts on the belt, elongation of the belt itself or looseness in the belt loops wound on the retractor reel, or both, can allow considerable slackening of the belt even though the lock mechanism, as intended, does prevent the reel from unrolling.
Since this problem of slackening of the belt has been found to be substantial with many known systems, various proposals for solving it have been made. According to one proposed solution, the belt is led out of the retractor via a roller which ims prevented from rotating when a reel engages a lock bar so that when a large force is applied to the seat belt, a friction between the seat belt and the roller minimizes further pulling out of the belt. Although the simple construction of this device is an advantage, it involves the problem of weakening of the seat belt because the belt is subject to abrasion and wear from moving along the roller. Since substantially the same portion of the seat belt tends to be brought under friction contact with the roller in normal use, the service life of the seat belt itself is reduced.
The present invention provides a novel device which solves the above-mentioned problems of previously known devices very effectively. In particular, a device, according to the present invention, comprises a clamp holder and a base member having closely spaced surfaces defining a narrow gap through which the belt passes and from which the belt runs off forwardly at an angle generally away from the base member. The clamp member carries a clamp having a belt gripping surface which is generally contiguous to but protrudes slightly from the surface of the clamp holder and defines part of the belt receiving gap. There are generally matching wedge surfaces on the clamp holder and clamp which are oriented forwardly obliquely and transversely to the belt-receiving gap and are adapted selectively to wedge the clamp into engagement with the belt upon an abrupt movement of the belt forwardly through the gap. The clamp holder is pivoted about an axis that is transverse to the direction of movement of the belt, spaced from the gap and located between the forward end of the gap and the rearward end of the gripping surface of the clamp. The clamp and clamp holder are resiliently urged about the pivot axis in the direction tending to move the nose portion of the clamp holder toward the surface of the base member and hold the clamp away from the belt.
Upon an abrupt force exerted on the nose portion of the clamp holder when the belt is pulled sharply, the clamp holder pivots in opposition to the spring force such that the clamp is moved into engagement with the belt, whereupon the clamp is pulled forward and is wedged toward the surface of the base and grips the belt against further forward movement.
One advantage of the device is that under normal movements of the belt as it is pulled out and retracted by the occupant or by some mechanism forming part of a passive restraint system, the belt moves easily over a smooth surface and is subject to little abrasion and wear. When the device operates in an emergency situation, on the other hand, the amount of surface area of the belt clamped between the clamp and the base surface is relatively large, thus affording effective restraint with a minimum of risk of causing the belt to break. Devices which grip a belt along a narrow band present a greater risk of belt breakage. Inasmuch as the device is entirely self-contained, it can easily be used in connection with a conventional retractor without any modification of the retractor. On the other hand, the device can readily be built into a retractor.
For a better understanding of the invention, reference may be made to the following description of an exemplary embodiment, taken in conjunction with the figures of the accompanying drawings.